U.S. patent number 7,078,074 [Application Number 11/065,113] was granted by the patent office on 2006-07-18 for lens plasma coating system.
This patent grant is currently assigned to Novartis AG. Invention is credited to Yasuo Matsuzawa, Lynn Cook Winterton.
United States Patent |
7,078,074 |
Matsuzawa , et al. |
July 18, 2006 |
Lens plasma coating system
Abstract
The invention provides a method for plasma coating of optical
lenses, particularly lenses made of silicone-containing polymer.
The method of the invention comprising selectively depressurizing
and pressurizing an entry hold chamber and an exit hold chamber
while constantly maintaining a plasma gas in a coating chamber at a
process pressure without depressurizing and pressurizing repeatedly
the coating chamber, wherein the coating chamber is located between
the entry hold chamber and the exit hold chamber.
Inventors: |
Matsuzawa; Yasuo (Roswell,
GA), Winterton; Lynn Cook (Alpharetta, GA) |
Assignee: |
Novartis AG (Basel,
CH)
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Family
ID: |
22846899 |
Appl.
No.: |
11/065,113 |
Filed: |
February 23, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050142287 A1 |
Jun 30, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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09911221 |
Jul 23, 2001 |
6881269 |
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60225940 |
Aug 17, 2000 |
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Current U.S.
Class: |
427/166; 118/719;
118/723R; 427/569; 427/570 |
Current CPC
Class: |
B05D
1/62 (20130101); B29C 59/14 (20130101); B29D
11/00009 (20130101); C23C 16/54 (20130101); B29C
2059/147 (20130101); B29L 2011/0041 (20130101); Y10S
414/139 (20130101) |
Current International
Class: |
B05D
5/06 (20060101); H05H 1/24 (20060101) |
Field of
Search: |
;427/569,570,165,166,164,167 ;118/719,723R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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34 15012 |
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Jan 1986 |
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DE |
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3415012 |
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Jan 1986 |
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DE |
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19808163 |
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Jul 1999 |
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DE |
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Primary Examiner: Meeks; Timothy
Assistant Examiner: Turocy; David
Parent Case Text
This application is a division of U.S. patent application Ser. No.
09/911,221 filed Jul. 23, 2001, now U.S. Pat. No. 6,881,269, which
claims benefits under 35 U.S.C. .sctn.119(e) of U.S. provisional
patent application No. 60/225,940 filed Aug. 17, 2000.
Claims
What is claimed is:
1. A method for treating the surface of optical lenses, said method
comprising the steps of: (A) providing a plasma coating system
comprising a coating chamber including a pair of spaced apart
electrodes disposed therein, an entry chamber upstream from the
coating chamber, and an exit chamber downstream from the coating
chamber, wherein the entry chamber includes an entry hold chamber
adjacent to the coating chamber, wherein the exit chamber includes
an exit hold chamber adjacent to the coating chamber, wherein each
of the coating chamber, the entry hold chamber, and the exit hold
chamber, independent of each other, is in communication both with a
negative pressure source and with a source of a plasma gas; (B)
preparing the coating chamber for coating the optical lenses,
wherein the step of preparing the coating chamber comprises (i)
filling the coating chamber with the plasma gas, (ii) constantly
maintaining the plasma gas in the coating chamber at a process
pressure by using the negative pressure and plasma gas sources of
the coating chamber, and (iii) maintaining a predetermined electric
potential at each said electrode so that a plasma cloud of said
plasma gas is established between said electrodes; (C) moving a
lens into said entry hold chamber; (D) sealing and vacuuming the
entry hold chamber with the lens for a period of time; (E) bringing
said entry hold chamber to said process pressure by filing it with
said plasma gas; (F) bringing said entry hold chamber into
communication with said coating chamber; (G) moving said first lens
from said entry hold chamber into said coating chamber and through
said plasma cloud; (H) introducing said plasma gas into said exit
hold chamber until reaching said process pressure; (I) bring the
exit hold chamber in communication with the coating chamber; (J)
moving said first lens from said coating chamber to said exit hold
chamber, (K) repeating the steps from step (C) to step (J) for each
lens to be treated, wherein the method is characterized in that the
coating chamber is not depressurized and pressurized
repeatedly.
2. The method as in claim 1, wherein said plasma gas is a
polymerizable gas.
3. The method of claim 2, wherein the plasma gas contains
oxygen.
4. The method as in claim 1, wherein the entry chamber comprises an
entry lock chamber upstream from the entry hold chamber, wherein
the entry lock chamber is in communication with but sealable off
from the entry hold chamber, wherein step (C) includes moving said
first lens into said entry lock chamber before moving it into the
entry hold chamber, wherein said method includes, following step
(C) but before step (D), the steps (L) bringing said entry lock
chamber and said entry hold chamber to a predetermined pressure,
(M) bringing said entry lock chamber into communication with said
entry hold chamber and moving said lens from said entry lock
chamber into said entry hold chamber, and (N) sealing said entry
hold chamber from said entry lock chamber.
5. The method as in claim 4, wherein said process pressure and said
predetermined pressure are unequal.
6. The method of claim 4, wherein the plasma gas contains
oxygen.
7. The method as in claim 1, wherein the coating chamber includes a
plurality of pairs of spaced apart electrodes, wherein the pairs
are tandemly arranged in said coating chamber.
8. The method as in claim 1, wherein said exit chamber has an exit
lock chamber, said exit lock chamber being downstream from and in
communication with said exit hold chamber, said method includes,
following step (J), the steps (L) evacuating said plasma gas from
said exit hold chamber, (M) bringing said exit lock chamber to a
pressure equal to the pressure in said exit hold chamber, (N)
bringing said exit hold chamber into communication with said exit
lock chamber and moving said lens from said exit hold chamber into
said exit lock chamber, and (O) sealing said exit lock chamber from
said exit hold chamber.
9. The method of claim 8, wherein the plasma gas contains
oxygen.
10. A method for applying a polymer coating to optical lenses, said
method comprising the steps of: (A) providing said optical lenses
on a plurality of carriers; (B) providing a plasma coating system
comprising a coating chamber including a plurality of pairs of
spaced apart electrodes disposed in tandem therein, an entry
chamber upstream from the coating chamber, and an exit chamber
downstream from the coating chamber, wherein the entry chamber
includes an entry hold chamber adjacent to the coating chamber and
entry lock chamber upstream from the entry lock chamber, wherein
the exit chamber includes an exit hold chamber adjacent to the
coating chamber, wherein each of the coating chamber, the entry
hold chamber, and the exit hold chamber, independent of each other,
is in communication both with a negative pressure source and with a
source of a plasma gas, wherein the plasma gas is a polymerizable
gas; (C) preparing the coating chamber for coating the optical
lenses, wherein the step of preparing the coating chamber comprises
(i) filling the coating chamber with the plasma gas, (ii)
constantly maintaining the plasma gas in the coating chamber at a
process pressure by using the negative pressure and plasma gas
sources of the coating chamber, and (iii) maintaining a
predetermined electric potential at each said electrode so that a
plasma cloud of said plasma gas is established between said
electrodes; (D) moving a carrier with optical lenses into said
entry lock chamber; (E) sealing said entry lock chamber and
thereafter bringing said entry lock chamber to a predetermined low
pressure; (F) bringing said entry hold chamber to said
predetermined low pressure; (G) opening said entry hold chamber to
said entry lock chamber and moving said carrier from said entry
lock chamber into said entry hold chamber; (H) following step (G),
sealing said entry hold chamber from said entry lock chamber,
introducing said plasma gas into said entry hold chamber until it
reaching process pressure; (I) following step (G), bringing said
entry lock chamber to ambient pressure, bringing another carrier
into said entry lock, and repeating said method beginning at step
(E) with respect to said another carrier and for a desired number
of subsequent carriers; (J) following step (H), opening said
coating chamber to said entry hold chamber and moving said carrier
into said coating chamber and through said plasma clouds; (K) after
said carrier is removed from said entry hold chamber in step (J),
sealing said entry hold chamber from said coating chamber and said
entry lock chamber and returning to step (F) with respect to said
another carrier; (L) following step (J), introducing said plasma
gas into said exit hold chamber until reaching said process
pressure; (M) bringing said exit hold chamber to said process
pressure; and (Q) moving said carrier from said coating chamber to
said exit hold chamber, wherein the method is characterized in that
the coating chamber is not depressurized and pressurized
repeatedly.
11. The method of claim 10, wherein the plasma gas contains
oxygen.
12. A continuous method for treating the surface of optical lenses,
said method comprising the steps of: (A) providing said optical
lenses in batches, (B) providing a plasma coating system comprising
a coating chamber including a pair of spaced apart electrodes
disposed therein, an entry chamber upstream from the coating
chamber, and an exit chamber downstream from the coating chamber,
wherein the entry chamber includes an entry hold chamber adjacent
to the coating chamber, wherein the exit chamber includes an exit
hold chamber adjacent to the coating chamber, wherein each of the
coating chamber, the entry hold chamber, and the exit hold chamber,
independent of each other, is in communication both with a negative
pressure source and with a source of a plasma gas, wherein the
entry hold chamber and the exit hold chamber, independently of each
other are sealable from other chambers, and (C) selectively
depressurizing and pressurizing the entry hold chamber and the exit
hold chamber with the plasma gas before bring them in communication
with the coating chamber while continuously maintaining the plasma
gas in a coating chamber at a process pressure between said batches
without depressurizing and pressurizing repeatedly the coating
chamber, maintaining a plasma gas in said coating chamber, wherein
said plasma gas is produced from a process gas containing oxygen.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a system for coating contact
lenses, or other optical lens devices, particularly those made of
silicone-containing polymer. Hereinafter the term silicone polymers
are used to indicate silicone-containing polymers suitable for
ocular uses, including rigid silicone polymers, silicone elastomers
and silicone hydrogels. The advantages of silicone polymers as
contact lens materials have long been recognized. However, silicone
polymers have several disadvantages. For example, certain materials
in the eye's tear film tend to adhere to the lenses and reduce
their optical clarity. The silicone lens, especially silicone
elastomer or hydrogel lens, may be tacky and this characteristic
may render the lens to stick to the cornea, and the material's
hydrophobic nature prevents the lens from wetting.
To resolve these problems, it is known to apply a very thin
hydrophilic coating using electrical glow discharge polymerization.
Generally, the coating process involves placing a silicone lens
core in, or moving it through, a plasma cloud so that the material
adheres to the core. Although various materials may be used,
hydrocarbons such as methane may be used.
The polymerized coating provides a highly wettable surface without
significantly, if at all, reducing the oxygen and carbon dioxide
permeability of the lens. It also provides an effective barrier
against tear film material that would otherwise adhere to the lens,
thereby preventing the optical clarity degradation that would
otherwise occur.
Conventional plasma polymerization lens coating techniques employ
batch systems in which one or more silicone lens cores are placed
in a reactor chamber between opposing electrodes. The chamber is
then sealed and depressurized by a vacuum system. Significant time
is required to pump the batch system to the operative pressure.
When a suitable pressure is achieved in the chamber, a process gas
is introduced into the chamber interior, and the electrodes are
energized. The resulting plasma cloud may apply a thin polymer
coating to the lens. After an appropriate time, the electrodes are
de-energized, and the reactor chamber is brought back to
atmospheric pressure so that the lenses may be removed.
It has been recognized that it is preferable to move the lenses
through the plasma cloud. Thus, in certain systems, the silicone
lens cores are mounted on a rotating wheel disposed between the
electrodes so that the wheel carries the lenses through the cloud.
These systems are sometimes described as "continuous" systems to
distinguish them from other batch systems. However, all such
systems are considered to be batch systems for purposes of the
present disclosure in that each requires a reactor chamber that
must be repeatedly pressurized and depressurized as one or more
groups of silicone lens cores are placed in and removed from the
system.
One example of a batch system is provided in U.S. Pat. No.
4,312,575 to Peyman et al., the disclosure of which is incorporated
by reference herein for all purposes. In "Ultrathin Coating Of
Plasma Polymer Of Methane Applied On The Surface Of Silicone
Contact Lenses," Journal of Biomedical Materials Research, Vol. 22,
919 937 (1988), Peng Ho and Yasuda describe a batch system
including a bell-shaped vacuum chamber in which opposing aluminum
electrodes are disposed. A rotatable aluminum plate sits between
the electrodes and is driven by an induction motor within the
system.
SUMMARY OF THE INVENTION
The present invention recognizes and addresses disadvantages of
prior art constructions and methods.
Accordingly, it is an object of the present invention to provide an
improved lens plasma coating system.
This and other objects are achieved by a system for treating the
surface of an optical lens. The system includes an entry chamber
having a first entrance gate and a first exit gate. The first
entrance gate and the first exit gate seal the entry chamber when
the gates are closed. The entry chamber includes a conveyor
extending between the first entrance gate and the first exit gate.
A first negative pressure source is in selective communication with
the entry chamber. A coating chamber has a second entrance gate and
a second exit gate. The second entrance gate and the second exit
gate seal the coating chamber when they are closed. The coating
chamber includes a pair of spaced apart electrodes disposed therein
and a conveyor extending between the second entrance gate and the
second exit gate so that the conveyor conveys the lens between the
electrodes. A source of plasma gas is in communication with the
coating chamber to introduce the gas into the coating chamber. A
second negative pressure source is in communication with the
coating chamber. An electrical power source is in communication
with the electrodes to apply a predetermined electrical potential
at each electrode so that, upon establishment of a predetermined
pressure in the coating chamber by the second negative pressure
source, a plasma cloud of the gas is established between the
electrodes. An exit chamber has a third entrance gate and a third
exit gate. The third entrance gate and the third exit gate seal the
exit chamber when they are closed, and the exit chamber includes a
conveyor extending between the third entrance gate and the third
exit gate. A third negative pressure source is in selective
communication with the exit chamber. The entry chamber communicates
with the coating chamber through the first exit gate and the second
entrance gate so that the entry chamber conveyor and the coating
chamber conveyor communicate to pass the lens from the entry
chamber to the coating chamber. The coating chamber communicates
with the exit chamber through the second exit gate and the third
entrance gate so that the coating chamber conveyor and the exit
chamber conveyor communicate to pass the lens from the coating
chamber to the exit chamber.
A method for treating the surface of an optical lens according to
the present invention includes providing first an optical lens and
providing a coating chamber including a pair of spaced apart
electrodes disposed therein. A plasma gas is maintained in the
coating chamber. A first predetermined pressure is maintained in
the coating chamber, and a predetermined electric potential is
maintained at each electrode so that a plasma cloud of gas is
established between the electrodes. An entry chamber is provided
upstream from the coating chamber, and the first lens is moved into
the entry chamber. Gas is introduced into at least a portion of the
entry chamber adjacent the coating chamber, and at least that
portion of the entry chamber is brought to the first predetermined
pressure. The entry chamber is brought into communication with the
coating chamber, and the first lens is moved from the entry chamber
into the coating chamber and through the plasma cloud. An exit
chamber is provided downstream from the coating chamber. Gas is
introduced into at least a portion of the exit chamber adjacent the
coating chamber, and at least that portion of the exit chamber is
brought to the first predetermined pressure. The first lens is
moved from the coating chamber to the exit chamber.
The accompanying drawings, which are incorporated in and constitute
a part of this specification, illustrate one or more embodiments of
the invention and, together with the description, serve to explain
the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
A full and enabling disclosure of the present invention, including
the best mode thereof, directed to one of ordinary skill in the
art, is set forth in the specification, which makes reference to
the appended drawings, in which:
FIG. 1A is a perspective view of a lens holding tray for use in a
lens coating system and method according to an embodiment of the
present invention;
FIG. 1B is an enlarged perspective view of the holding tray as in
FIG. 1A;
FIG. 1C is a cross-sectional view taken along the line 1C--1C in
FIG. 1B;
FIG. 2 is a perspective view of a lens tray carrier and a slug
(i.e. carrier holding system) for use in a lens coating system and
method according to an embodiment of the present invention;
FIG. 3, presented on separate drawing sheets as FIGS. 3A and 3B, is
a schematic illustration of a lens coating system according to an
embodiment of the present invention;
FIG. 4A is a partial perspective view of a lens coating system
according to an embodiment of the present invention;
FIG. 4B is a cross-sectional view taken along the line 4B--4B in
FIG. 4A;
FIG. 4C is a partial perspective view of a lens coating system
according to an embodiment of the present invention;
FIG. 5A is a partial perspective view of a lens coating system
according to an embodiment of the present invention;
FIG. 5B is a cross-sectional view of a chamber and valve as shown
in FIG. 5A;
FIG. 6A is a cross-sectional view of a lens coating system
according to an embodiment of the present invention; and
FIG. 6B is a plan view of the interior magnetic arrangement of a
magnetic device for use in a coating chamber of a lens coating
system according to an embodiment of the present invention.
Repeat use of reference characters in the present specification and
drawings is intended to represent same or analogous features or
elements of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Reference will now be made in detail to presently preferred
embodiments of the invention, one or more examples of which are
illustrated in the accompanying drawings. Each example is provided
by way of explanation of the invention, not limitation of the
invention. In fact, it will be apparent to those skilled in the art
that modifications and variations can be made in the present
invention without departing from the scope or spirit thereof. For
instance, features illustrated or described as part of one
embodiment may be used on another embodiment to yield a still
further embodiment. Thus, it is intended that the present invention
covers such modifications and variations as come within the scope
of the appended claims and their equivalents.
The present invention is directed to an optical lens coating system
in which lens cores may enter, pass through and exit the system
without requiring the coating zone to be repeatedly pressurized and
depressurized. Although the discussion herein describes the use of
a methane containing plasma cloud to apply a hydrophilic polymer
coating to silicone lens cores, it should be understood that this
is for exemplary purposes only and that other plasma and lens
materials may be used. For example, the system may employ any
suitable plasma, whether generated of hydrocarbon or other
appropriate material, that would apply a desirable coating on a
lens core. Additionally, the plasma may be comprised of an
oxidizing gas so that the lens core surface is oxidized to create a
hydrophilic layer. As used herein, a "coating" includes such a
layer. Further, the system may be used in conjunction with lens
cores made of any material upon which it is desirable to place a
coating. Thus, it should be understood by those skilled in this art
that the description of silicone lens cores and methane plasma
herein is not intended to limit the scope or spirit of the present
invention.
Furthermore the system may use any suitable apparatus and method
for generating plasma to treat lens cores. Such apparatus and
methods should be understood by those skilled in the art and are
therefore not discussed in detail herein. Thus, it should also be
understood that the particular arrangement described below for
generating plasma is provided for exemplary purposes only.
Prior to entering the system, referring now to FIG. 1A, the lens
cores are placed in a holding tray 10 having an outer frame 12 and
vertical intermediate members 14. FIG. 1A illustrates an exemplary
holding tray. Seven rows of wire holders 16 extend between each
adjacent vertical member. In the two outer columns 18 and 20, each
row contains four holders, while each row in the two inner columns
22 and 24 includes three holders. Thus, the tray includes
ninety-eight holders in all.
Referring to FIGS. 1B and 1C, each holder 16 includes an annular
wire rim 26 and five wire stems 28 extending radially inward
therefrom. A lens core 30 is placed in each holder so that it sits
on the stems 28. Holder 16 is described in more detail in
commonly-assigned U.S. Pat. No. 5,874,127, the entire disclosure of
which is incorporated by reference herein.
Referring again to FIG. 1A, and also referring to FIG. 2, each
holding tray 10 includes a pair of hooks 32 on the opposing outer
vertical members 14 of frame 12. Corresponding hooks 34 on a tray
carrier 36 receive hooks 32 so that holding tray 10 may be hung on
the tray carrier. In the embodiment shown in FIG. 2, carrier 36 may
hold four holding trays 10 and, therefore, up to three hundred
ninety two lens cores.
Referring now to FIGS. 3A and 3B, the tray carrier is placed into a
linear plasma coating system 40. Initially, the trays move through
a drying chamber comprised of five subchambers (hereinafter
referred to as "zones") 42A 42E, each approximately five meters
long. The tray carrier remains for a total of about twenty minutes
in the drying chamber for a desired time, say about twenty minutes
or sufficient to meet the necessary vacuum and coating application
target.
Because the lens cores may contain a hydrophilic material, they can
be hygroscopic and therefore can absorb water from the environment.
Thus, it may be desirable to allow drying time. The dry zones
maintain a constant relative humidity level, e.g., at or below ten
percent to permit further drying, if necessary, and also provide a
dry buffer area in which to place lens cores prior to entering the
coating zones.
Referring also to FIGS. 2, 4A and 4B, each tray carrier is received
in a rectangular slot 44 defined as a "slug" 46. A pair of bolts
secures the carrier in the slug. A bore 48 extends through slug 46
beneath the tray carrier. The drying chamber includes a conveyor to
transport the slug and carrier (hereinafter referred to
collectively as the "carrier" unless otherwise indicated). The
conveyor is comprised of individual conveyors in the zones 42A 42E,
each extending between opposing wheels 52 and 54. A servo motor 56
drives the conveyor and may be controlled by a personal computer,
main frame system or other programmable logic circuit (hereinafter
referred to generally as "PLC"). Two side members 58 sit on
respective sides of the conveyor, and rollers 60 are disposed in
gaps 62 in each side member to guide the tray carrier as it passes
between the side members.
A light source 64 mounted in one side member directs light across
to the other side member, where it is detected by a light detector
66. The light source and light detector are aligned so that light
passes between them through bore 48 in slug 46. Light detector 66
outputs a signal to the PLC which, in turn, controls servo motor
56. Accordingly, the PLC detects the carrier's presence as the slug
initially breaks the light beam between source 64 and detector 66
upon entering the first dry zone 42A. Other carrier detection
systems may be utilized in lieu of the light detector; for example
pressure or contact microswitches may also be employed. When bore
48 reaches the light source/detector pair, detector 66 again
detects the light beam, and the PLC stops servo motor 56 for an
approximate preprogrammed time say four minutes. At the end of this
time, the PLC again activates motor 56 so that the carrier is
passed to the second dry zone, 42B. Dry zone 42B has a conveyor,
motor and side member pair like that of zone 42A, except that an
additional mechanism is included in zone 42B to rotate the side
members and conveyor ninety degrees so that the carrier may be
passed to zone 42C. In each zone, however, a light source/detector
pair is provided to detect the presence of a carrier in the zone.
The PLC moves the carrier from one dry zone to the next if no
carrier is still waiting in the subsequent zone.
The entrance to zone 42A may be open or may have a suitable
covering as appropriate for a given system. A respective duct 68
feeds from a suitable air handling system (not shown) and directs
the conditioned air or gas to each dry zone. Suitable ventilation
ducts may also be provided. The air conditioning system may be
independently controlled to continuously provide properly
temperature-controlled and humidified air to the ducts, e.g., at
approximately 70.degree. F. +/-2.degree..
Referring again to FIGS. 3A and 3B, the PLC moves the carrier
through a slit valve 72 into an entry lock 70 if the carrier has
been in dry zone 42E for a sufficient duration, if no carrier is
waiting in entry lock 70, and if suitable conditions exist in entry
lock 70 as described in more detail below. Entry lock 70 includes a
conveyor 50 and side members 58 as in the dry zones. A light
source/detector pair is also provided so that the PLC senses when
the carrier is fully within the entry lock. The PLC then stops the
servo motor that drives the conveyor and closes the slit valves at
the entry lock's entrance and exit to seal the entry lock.
Referring also to FIGS. 5A and 5B, the entrance slit valve 72
includes a door 74 having a sealing material 76 that lines the
periphery of its inside surface. Door 74 is hinged so that it is
movable by a linkage 78 between an open and closed position. The
PLC controls linkage 78. When the door is in its closed position,
seal 76 surrounds and seals an entrance passage 80 into entry lock
70.
When the light source/detector in entry lock 70 detects the
presence of the carrier through bore 48 (FIG. 2), the PLC closes
the slit valves at both ends of entry lock 70. The entry lock is a
stainless steel chamber with which inlets, outlets and sensors may
communicate as discussed below. It is a closed chamber except for
the slit valves. Thus, when the valves are closed, the entry lock
is sealed.
When the carrier is in the entry lock, and the chamber is sealed,
the PLC activates a valve 82 and a pump 84 to pump out the entry
lock and thereby create a vacuum condition therein. Specifically,
the pump brings the interior area of entry lock 70 from ambient
pressure to a desired preset lower pressure, e.g., at or below one
mTorr. The PLC monitors the entry lock's pressure by a pressure
sensor 85 extending through the entry lock's housing.
It should be understood that while the entry lock housing, as well
as the housings of the entry hold, entry buffer, coating, exit
buffer, exit hold and exit lock chambers discussed below, may all
made of stainless steel, the housings may be made of any suitable
material and in any suitable construction. Further, the housings
for the five dry zones and of the five exits zones discussed below
may be made from a rigid polymer such as polymethylmethacrylate
(PMMA), but may also be made from steel or other suitable
material.
When the PLC is notified from pressure sensor 85 that the interior
pressure of entry lock 70 is at or below the preset lower pressure,
and that a preset minimum time has lapsed, say 290 seconds, since
valve 82 was activated, the PLC opens slit valve 86 between entry
lock 70 and an entry hold chamber and activates the conveyors in
both the entry lock and the entry hold so that the carrier is moved
into the entry hold.
The entry hold also includes vertical side members and a light
source/detector pair. When the slug bore 48 (FIG. 2) aligns with
the light detector and thereby indicates to the PLC that the
carrier is fully in the entry hold, the PLC closes slit valve 86
and a slit valve 90 to seal the entry hold. After closing valve 90,
the PLC activates a valve 92 that opens a gas line 94 connected to
a source (not shown) of dry gas, e.g., nitrogen, to the interior of
entry lock 70. The PLC continues to vent the entry lock with the
dry gas until pressure sensor 84 indicates atmospheric pressure in
the entry lock. The PLC then opens slit valve 72 so that the entry
lock can receive the next carrier.
The gas is "dry" in that it has a low water content, for example
less than three ppm. A dry vent gas is preferred to prevent
undesired water absorption by the lens cores or the chamber walls.
In a preferred embodiment, a single source of dry gas is used to
provide the vent gas to line 94 as well as to the vent lines for
other chambers downstream from the entry lock. Thus, it should be
understood that while the chambers are referred to herein as having
"respective" vent sources, this includes a construction where all
the vent lines may be fed by the same ultimate source of vent gas.
Similarly, while individual vacuum pumps are shown in FIG. 3 and
described herein, it should be understood that pumping lines to
multiple chambers may communicate with the same source of negative
pressure.
Before opening valve 86, the PLC brings entry hold 88 to a pressure
less than or equal to the set low pressure by activating a valve 98
that opens the entry hold interior to a vacuum pump 100. When
pressure sensors 85 and 102 indicate that the entry lock pressure
and the entry hold pressure are equal, +/-5 mT, the PCL opens slit
valve 86 to move the carrier into the entry hold.
Despite the prior drying stages, the lens cores may still contain
some water. The entry hold therefore acts both as a buffer and a
drying stage. Repeated pumping to create vacuum conditions in the
entry hold draws water vapor from the chamber's walls, and
potentially from lens cores, thereby creating a dry environment.
Dry gas is used to vent the chamber through a valve 104 operated by
the PLC to maintain this condition. When the carrier enters the
entry hold, and the PLC seals the chamber, valve 98 remains open so
that pump 100 draws water vapor from the tray carrier, slug and
lens cores.
When the PLC determines that when sufficient time has elapsed since
closing slit valves 86 and 90, it closes valve 98 and opens a valve
106 between a mass flow controller 108 and the entry hold interior.
The mass flow controller, the construction and operation of which
should be understood by those skilled in the art, may be controlled
independently of the PLC in this embodiment and introduces process
gas from a common line 110 into the entry hold.
When pressure sensor 102 indicates that the internal pressure of
entry hold 88 is approximately the desired level, the PLC opens
slit valve 90 and activates the conveyor motors in the entry hold
and in an entry buffer 112 to move the carrier into the entry
buffer. Again, the entry buffer includes vertical side members 58
and a light source/detector pair that enables the PLC to determine
when the slug bore aligns with the light source and detector,
thereby indicating that the carrier is fully within the entry
buffer. The PLC then closes slit valve 90 and continues to pump the
entry hold through valve 98 until the entry hold reaches the
desired preset lower pressure. At that time, provided the other
conditions discussed above are also met, the PLC opens the slit
valve 86 and moves the next carrier into the entry hold.
The entry buffer helps isolate the downstream coating zone from
non-process gasses that might otherwise flow to the coating zones
from the entry hold. It also acts as a waiting chamber for a
carrier waiting to enter the coating zones. It is maintained at the
process pressure through a valve 114 that is controlled by the PLC
and that opens the entry buffer to a vacuum pump 116. The PLC
monitors pressure in the entry buffer by a pressure sensor 118 and
introduces the process gas to the entry buffer through a valve 120
connected to process gas line 110 through a mass flow controller
122. When necessary, the PLC can vent the entry buffer with dry gas
through a valve 124.
From the entry buffer, the carrier moves through tandem coating
zones 126 and 128. The PLC maintains the coating zones at
approximately the process pressure by pressure valves 130 and 132
that expose the coating zone interiors to the vacuum pumps 133 and
134. The PLC provides process gas to the coating zones by valves
136 and 138 that are connected to process gas line 110 through mass
flow controllers 140 and 142. While a single valve/mass flow
controller is shown in this embodiment for each coating zone, it
should be understood that a respective such pair may be provided
for the front half and the back half of each chamber to
independently control the flow of gas to each half. If necessary,
the PLC can vent the coating zones with dry gas through valves 144
and 146. The PLC monitors pressure in the coating zones through
pressure sensors 148/149 and 150/151.
An exit buffer 152 follows the second coating zone 128. As with the
entry buffer and the coating zones, it includes a conveyor and
servo motor that may be operated by the PLC. It also includes
vertical members 58 and a light source and detector pair. The PLC
maintains the process pressure level in the exit buffer through a
valve 154 opening to a vacuum pump 156. The PLC monitors pressure
in the exit buffer through a pressure sensor 158 and controls the
flow of process gas from line 110 into the exit buffer from a mass
flow controller 160 by a valve 162.
There are no slit valves between entry buffer 112 and first coating
zone 126, between first coating zone 126 and second coating zone
128, or between second coating zone 128 and exit buffer 152.
Instead, several steel shoulders 164 extend partially laterally
into the system to create a channel extending from the entry buffer
through the two coating zones to the exit buffer. Thus, the entry
buffer chamber, coating zones and exit buffer chamber define a
segmented common chamber. As noted above, the PLC maintains this
common chamber at the process pressure, and maintains process gas
in the chamber, during the system's operation through respective
valves and mass flow controllers. Because of the selective
pressurization and depressurization of the entry hold discussed
above, and of the exit hold discussed below, the system may coat
lens cores on successive tray carriers without having to pressurize
and depressurize the coating zones.
The illustrated coating zones 126 and 128 are identically
constructed. For ease of explanation, therefore, only the structure
of coating zone 126 is described herein.
Coating zone 126 includes two tandemly arranged magnetrons, each
having a pair of opposing electrodes 166 and 168. The use of a
magnetron is optional, depending on the application. Referring to
the schematic cross-sectional view in FIG. 6A, the coating zone
does not include vertical members 58 (FIGS. 4A 4B) that would
otherwise interfere with the application of the plasma cloud to the
lens cores. The cloud is created by electrodes 166 and 168, which
include rectangular titanium plates 170 and 172. Each titanium
plate is separated from a respective magnetic device 174 and 176 by
four 2 mm 3 mm ceramic buttons 178. Each titanium plate is
approximately 50 centimeters high, 1/16 inches thick and 18
centimeters long.
Each magnetic device 174 and 176 may include an outer metal box,
for example made of stainless steel, through which cooling water
may be pumped from tubes 180. Referring also to FIG. 6B, the
interior of each box includes a rectangular central steel core 182
and a surrounding rectangular steel ring 184. A series of permanent
magnets 186 extend between core 182 and ring 184 and are arranged
in a north-south pattern as shown in FIG. 6B so that central core
182 is a magnetic "south" pole and outer ring 184 is a magnetic
"north" pole. Although the exact opposite can also be employed,
i.e., the north/south magnets may be totally reversed. Each
permanent magnet is separated from adjacent parallel magnets by an
approximately two inch gap. Titanium plates 170 and 172 are driven
to the same electric potential by an AC power source 188 through a
transformer 190. The strength of the magnets may be varied to
control the extent of the plasma by one skilled in the art.
A distance of approximately seven to ten centimeters separates
titanium plates 172 and 178. When energized, the plates create a
plasma cloud between them as should be understood in the art. The 2
mm 3 mm gap between the titanium plates and their respective
magnetic devices is so small, however, that no sufficient plasma
occurs there. The magnetic field created by the magnetic devices
behind the titanium plates also prevents plasma formation. This
creates a predictable, stable and relatively uniform plasma cloud
between the plates. While an intensely glowing rectangular plasma
area 188 is created immediately in front of each of the titanium
plates, a plasma cloud 190 between areas 188 has less plasma
definition but more uniformity. Specifically, it is more uniform in
the vertical direction. Cloud 190 sits above conveyor 50, and it is
therefore through this cloud that the lens cores are moved.
Referring again to FIGS. 3A and 3B, each electrode pair 166/168
includes its own pressure sensor 148/149 and vacuum throttle valve
130. As noted above, each electrode pair may also include its own
process gas throttle valve. The PLC constantly monitors the
pressure in the area in which each electrode pair is disposed and
adjusts valves 130 and 136 accordingly to maintain the processing
pressure condition. That is, in one embodiment, the process gas
flow rate into the area is constant. Throttle valves 130, however,
are set to the processing pressure and, therefore, control the out
flow rate to maintain the desired pressure. Thus, the uniform
plasma clouds remain consistent from one electrode pair to the
next. Further, the process gas inlet from each valve 136 is placed
behind one of the electrodes 166 or 168 so that the flow from the
process gas line is blocked by the electrodes and does not disturb
the plasma cloud. Other gas diversion schemes may be designed that
accomplish the same end, but using the electrode pair is a
convenient solution.
In one embodiment of the present invention, the process gas is
seventy percent methane and thirty percent air (a dry mixture of
nitrogen and oxygen). It was been found that including oxygen in
the process gas provides highly useful means for maintaining the
reaction (plasma) chamber clear of deposits such that the coating
zone does not have to be cleaned routinely. As can be appreciated,
in a continuous plasma apparatus, it is highly advantageous to
utilize a processing gas that prevents or diminishes deposits from
accumulating in the coating chamber, especially on the
electrodes.
As noted above, coating zones 126 and 128 do not include vertical
members or light source/detector pairs. Instead, the PLC runs the
servo motors in each zone at a constant speed so that the
respective conveyors run continuously at preset desired speed, say
five m/sec. Thus, once a carrier is driven onto the conveyor in
zone 126 from the conveyor in the entry buffer, it moves
continuously through the four magnetrons in the two coating
zones.
The PLC begins a timer when the light detector in the entry buffer
indicates that a carrier moves from the entry buffer conveyor to
the conveyor in the coating zone 126 and sends a subsequent carrier
from the entry buffer into the coating zone only upon expiration of
this timer. In one preferred embodiment, the length of the timer is
three hundred seconds, which provides enough time for the exit
buffer to move a downstream carrier to an exit hold chamber 196,
thereby preventing carriers from stacking up in the coating
zones.
Exit hold 196 is the mirror of the entry hold. The PLC creates a
vacuum by a pump 198 through a valve 200. It monitors pressure in
the exit hold by a pressure sensor 202 and controls the
introduction of process gas from line 110 and a mass flow
controller 204 by a valve 206.
When pressure sensor 202 indicates that the exit hold pressure is
approximately the coating zone pressure say fifty mTorr, and the
light detector in exit buffer 152 indicates that a carrier is
present in the exit buffer, the PLC opens a slit valve 208 between
the exit buffer and the exit hold and activates the conveyors in
the exit hold and exit buffer to transfer the carrier to the exit
hold. When the light detector in the exit hold-determines that the
transfer is complete, the PLC closes slit valve 208 and a slit
valve 210 at the exit hold's downstream end, thereby sealing the
exit hold. The PLC then throttles valve 200 to remove the process
gas and bring the exit hold to less than or equal to one mTorr, or
some other desired vacuum pressure.
An exit lock chamber 197 is downstream from the exit hold. Prior to
opening slit valve 210, the PLC pumps the exit lock to a pressure
of less than or equal to the set low pressure by throttling a valve
210 controlling the application of a vacuum pump 212 to the exit
lock interior. When the PLC determines from pressure sensor 202 and
a pressure sensor 214 in the exit lock that the exit hold pressure
and the exit lock pressure are approximately equal and at or less
than the set low pressure, it opens slit valve 210 and activates
the exit hold and exit lock conveyors to move the carrier to the
exit lock. At this point, the PLC closes slit valve 210 and a slit
valve 216 and vents the exit lock with dry gas by throttling a
valve 218 until pressure sensor 214 indicates that the exit lock
pressure has reached an ambient level. If the PLC detects an
ambient pressure condition in the exit lock and that a carrier is
present in the exit lock, it opens slit valve 216 and activates the
conveyors in the exit lock and a first exit zone 220A to move the
carrier to the exit zone. When a light detector in the exit zone
indicates that the carrier has been transferred, the PLC closes
slit valve 216 and pumps exit lock 197 back to the set low pressure
to receive the next carrier.
The construction of the exit zones 220A 220E is similar to that of
dry zones 42A 42E. They may be removed from the final zone 220
manually or by an automatic system so that the now-coated lenses
exit in the holders 16 (FIG. 1).
It should be understood that the above discussion presents one or
more preferred embodiments of the present invention and that
various suitable embodiments may fall within the scope and spirit
of the present invention. The embodiments depicted are presented by
way of example only and are not intended as limitations upon the
present invention, and it should be understood by those of ordinary
skill in the art that the present invention is not limited to such
embodiments since modifications can be made. Therefore, it is
contemplated that any and all such embodiments are included in the
present invention as may fall within the literal or equivalent
scope of the appended claims.
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